Vehicles, such as diesel-electric locomotives, may be configured with truck assemblies including two trucks per assembly, and three axles per truck, for example. The three axles may include at least one powered axle and at least one non-powered axle. The axles may be mounted to the truck via lift mechanisms, such as suspension assemblies including one or more springs, for adjusting a distribution of locomotive weight (including a locomotive body weight and a locomotive truck weight) between the axles.
As the vehicle travels along the rails, the amount of load on each of the axles of the truck can vary, with each axle also having a maximum load weight. In certain conditions, such as during inclement weather, proper traction with the track may be lost, thereby resulting in one or more wheels slipping. Accordingly, the tractive effort for these vehicles may be less than optimized. For example, the tractive effort may be affected on trains, particularly for heavy trains or hauls, during start-up, on inclines, and during adverse rail conditions, such as caused by inclement weather or other environmental conditions.
In known rail vehicle systems, the springs of the suspension systems for the trucks are preloaded. For example, each of the springs is preloaded based on a normal amount of weight to be supported by the suspension system for the axles. As a result, under certain conditions, the preloaded springs may not provide the sufficient normal force to maintain proper contact between the wheels of the truck and the track, especially during inclement or adverse rail conditions.